Cobalt base alloys and resistance elements formed therefrom



y 2, 1950 E s GREINER 2,506,420

COBALT BASE ALLOYS AND RESISTANCE ELEMENTS FORMED THEREFROM Filed Aug. 21, 1947 Q RES/SMNCE WIRE FORMED 0F COBALT- MANGANESE SOL/D Q SOL UT/ON Q /N VE N TOR E. 5. GEE/NEE A TTORNEV Patented May 2, 1950 UNITED STATES .ATENT OFFICE (JOBA'LT BASE ALizOYS 7 AND "RESISTANGE ELEMENTS FORMED THEREFROM :Earl S. Greiner, ShortiHills N. J., assignorto Bell Telephone Laboratories, Incorporated, New York, N. Y., aacorporation of New York Application August 21, 1947, Seflal N0.'-769,7'75

This invention relates to novel metal alloys 11seiful :ior forming electrical resistance -,elements, to

electrical resistance elements formed from such I alloys and to electrical devices embodying such mesistanceelements.

in the ,formation of electrical resistance ele ments, particularly those in the iorm of a fine awireasuch as .a wirelof mils L01 less in diameter, the ifollowing properties, among others, are important in the alloy .trom which the element is termed:

.l. A nelativelyihigh.electrical'resistivity 2. Satisfactory .ftensile strength 3. The ability to be mechanically worked as by :swaging or :by drawing into a'Wi-re .4. Stability .of electrical properties 'with time 15. .An electrical resistivity vindependent .of .previous thermal history. 7

accordance with the :present invention ecle- :sirable combinations of these properties are achievedtthroughthe usezofialloys .Which are solid :solutions of cobalt and manganese, preferably [containing :minorzproportions vof additionalingre- -tlients, also am solid solution, for "the :purpose 01 increasing electrical :resistance and appropriately modifying the :physical and :metallurgical prop- -erftles.

In the accompanying drawing isshown, in front elevation, :a conventional vwi-re wound resistor -WhiChFJSiOI1 type :of devicefin which the resistance elements and resistance alloys of .the present innention imayibe employed. in this drawingvare sls'tanne wire :I made .i-n-a'ccordance with the pres- ;ent invention is Wound upon .a ceramic "base 2. :is obvious :that the invention "is adaptable :to ithe formation :of :other :wire wound resistance idewices,;such as potentiometer cards, and that the aformation of resistance elements other than re- :sistancemires ar encompassed within the scope mfzthe presentinvention.

llitlias zbeen iiound'ithat :an alloy of substantially -the;iollo.wing composition :is outstanding for the iiormation of fine resistance wires:

composition may be made of substantially pin'e ingreolients or can be 'made of commercial grade ingredients "containing incidental impurities, which preferably do not "exceed 2 per cent and are ordinarily less than 1 per cent.

this al oy d, rafter iho swagins t approximately /4 inch n diame er and .coldswasins to 7.1 inch incli me er, ibe .s lliidrawn. A wire-drawn in this manner o -06 inch in diame er po sessed :a'resistivity at 520--:C,. {of 1,19 :microhmacentimeters. That th resistivity of the alloy is independent of thermal treatment is shown vJoy the yfact that a deviation in :the esistivity no greater than plus or minus 2 microhm-oentimeters was pr duced by any of the zzfzollowins treatments :of the drawn wire:

a. Heat-ins a 100 Q fior :67 zboursifollowed by noolingin air,

1). :Heating at l620 ;C. ior 2.4 hours liollowecl y cooling in air,

:0. Heating at 800 cooling-inair,

,d. -Heati n g at c990 .0. ,:for ;1 minute riollowed :by quenchinsin 0111- 'Ilhe temperature coeflioient of resistinit of the alloy was found to :be ,.?6l); l -li0- :per degree be- :tween 130 C. and 5100 The :alloyalso possesses the above-enumerated desirable properties of a resistance alloy. .I'he *wire of 406 inch in diameter referred to above Was iurther cold iclrawn ito a :diameter of '6 mils without difiiculty.

Alloys of similar composition haying somewhat :varied proportions will be found to have similarly desirable properties. A suitable range .of proportions or these ingredients is the rollowing-z C- :for 5 minutes .ifollowed y Other alloys which are solid solutions made up primarily of cobalt and manganese are also desirable 'for the formation of resistance elements.

The cobalt insuch alloys s'hou-ldbe present in an amount'in which it will retain the manganese -in solid solution and for that reason the cobalt should ordinarily be-present in an amount of at "least 45 per cent'by weight ofthe total cobalt and manganese. In order to provide a desirable --r'esisitivity the manganese should 'bepresent in an amount of at least 5 per-cent by weight of the combined cobalt and manganese. Preferably the manganese is present in an amount of-at least 20 per cent by weight of the total cobalt and manganese.

"It is not ordinarily desirable that ingredients -other than cobalt and manganese entering into the alloys 'bepresent in amounts greater than E5 in cylindrical 'bar inch in diameter cast from per cent byaveig'ht of -the'alloy. Pref era'b'ly-'suc"h ingredients do not exceed 10 per cent of the weight of the alloy. Any additional ingredients which are present should enter into solid solution. They may act to improve the resistivity, improve the physical and metallurgical properties ences in a 60Co-40Mn alloy is -1.8 or roughly 2. The following table shows the effect on resistivity of substituting iron, chromium, copper and aluminum for a small proportion of the co- 5 balt in the alloy referred to above.

i I 5 i Valence Dif- Change in Percent by Percent by wg f g Resistivity Valence of gggg x gi i z g Mweight g tf g Modifying g gigg g in Mierohmgigg gfl Elemen t and gercent of anganese Element centimeters 60Co-40Mn Modifying Alloy Element 40 60 Q 83 83 40 50 lOFe 84 83 2 0 40 501 94 93 4 2 1. 8 40 55 5C. 93 92 +1 3 2 40 58 2A1 100 100 +3 5 4. 1

or reduce the cost of the alloy, or they may even be without substantial eiiect.

An alloy made up of 82.1 per cent by weight of cobalt and 17.9 per cent by weight of manganese, when swaged and drawn from a cast bar inch in diameter to a wire having a diameter of .06 inch as described above, had a resistivity of '71 microhm-centimeters at 20 C. and a temperature coefficient of resistivity of 610x i0 per degree C. between 30 C, and 100 C. An alloy made up of 63.3 per cent by weight of cobalt and 36.7 per cent by weight of manganese, when cast into a inch diameter bar, hot swaged to a diameter of A; inch then cold swaged to .1 inch in diameter, had a resistivity of 83 microhmcentimeters at 20 C. and a temperature coefficient of resistivity of 6 l.0 10- per degree C. between 20 C. and 100 C. This alloy was capable of being cold drawn.

The basic cobalt-manganese solid solution may be modified with up to about per cent by weight of any additional element which enters into solid solution. Preferably additional elements are added which substantially increase the resistivity of the alloy although the addition of other ingredients which do not have this effect but which improve the physical properties of the alloy or reduce its cost may also be desirable.

It has been found that the greater the amount by which the valence of the added ingredients differs from the weighted average of the valences of the cobalt and manganese in the alloy, the greater is the effect of the added element in increasing th resistivity of the alloy. The weighted average of the valences is the sum of the product of the valence of the cobalt and the atomic fraction of cobalt in the total cobalt and manganese and the product of the valence of the manganese and the atomic fraction of manganese in the total cobalt and manganese. The term valence is used in this connection to mean the number of electrons relative to the closed :1 shell of the solute. In other words, it is the difference between 10, which is the number of electrons in the closed d shell and the number of electrons in the unfilled d shells of the transition elements or the number of valence electrons in the non-transition elements. (The ,s electrons of the transition elements are regarded as having been moved into the d shell.)

The effect of valence difference upon resistivity is clearly shown by comparing the resistivity of an alloy consisting of 60 per cent by weight of cobalt and 40 per cent by weight of manganese with the resistivities of similar alloys in which small proportions of the cobalt are replaced by modifying ingredients. valence of cobalt is 1 and the valence of manganese is -3 the weighted average of these val- Since the In this table the column headed Resistivity gives the actual measured resistivity for the alloy in microhm-centimeters. The column headed Corrected resistivity gives the calculated resistivity of an alloy containing the same amount of modifying ingredient in which the ratio of cobalt to manganese is 60 to 40 in place of the slightly lower ratio actually present in the alloy.

It may be seen from the table that iron which has a valence of 2, which is not significantly diiferent from that of the basic cobalt-manganese alloy, has no substantially effect upon the resistivity. Chromium, copper and aluminum which have valences diflering from the cobaltmanganese alloy by 2, 3 and 5, respectively, increase the resistivity by 1.8, 2 and 4.1 microhmcentimeters, respectively, per atomic per cent of added element.

Thus where a higher resistivity is sought than is possessed by an alloy containing cobalt and manganese alone, this may be achieved by incorporating in the alloy at modifying element which enters into solid solution and which has a valence which differs by at least 1 from the weighted average of the valences of the cobalt and manganese in the cobalt-manganese alloy. Although iron, as indicated above, produces no significant increase in the resistivity of a 60Co-40Mn alloy, the addition of iron to these alloys, as well as to other alloys containing cobalt and manganese, will often be found advantageous since it will materially lower the cost of the alloy.

The above-indicated increase in resistivity per atom per cent of added modifying element decreases as the total amount of modifying ingredient increases. The eifect of the addition of more than one resistivity increasing element is additive. This is illustrated by observing the efiect upon the resistivity caused by substitutin small amounts of other modifying ingredients for a part of the cobalt in the alloy listed in the table above which is made up of 4.0 per cent manganese, 58 percent cobalt and 2 per cent aluminum. When 60 2 per cent of silicon (which differs in valence from the 60C040Mn alloy by 6) is added to this alloy in place of a corresponding amount of cobalt, the corrected resistivity of the resulting alloy quenched from 980 C. is 115 microhmcentimeters as compared to 100 mlcrohm-centlmeters for the alloy containing no silicon.

When 5 per cent copper is added to the aluminum-containing alloy, the corrected resistivity is 109 microhm-centimeters as compared to 100 microhm-centimeters for the alloy containing no copper and as compared to a corrected resistivity of 92 microhm-centimeters for the corresponding copper-containing alloy which contains no aluminum. 15 When 10 per cent iron is added to the aluminum-containing alloy, the corrected resistivity is 93 microhm-centimeters as compared to 100 microhm-centimeters for the aluminum-containing alloy without iron, and as compared to a corrected resistivity of 83 microhm-centimeters for the corresponding iron-containin alloy without aluminum. It will be seen that in the latter case the additionbf aluminum to the iron alloy increases the resistivity considerably. On the other hand, the addition of iron to the aluminum-containing alloy decreases the resistivity because it dilutes the effect of the aluminum by increasing the total amount of modifying ingredient which is present.

Each of the specific alloys above, as well as other alloys containing these ingredients in different proportions, is useful as a resistance alloy. All of those alloys referred to above, except that containing silicon, are capable of being cold drawn to wires. The silicon-containing alloy, although not as workable as the other alloys, is capable of being hot or cold swaged. All of the alloys referred to above may be formed of substantially pure ingredients or of ingredients of commercial quality containing incidental impurities, which will ordinarily not exceed 2 per cent by weight and which will preferably not exceed 1 per cent of the alloy.

Any other modifying ingredients in addition to or in place of the iron, chromium, copper, aluminum and silicon referred to above, may be employed which are capable of entering into solid solution with the cobalt and manganese. When modifying ingredients are added it is des rable that they be present in amounts of at least 1 per cent by weight in order to exert a reasonable effeet on the alloy. As indicated above, it is not desirable that the modifying ingredients be added in amounts greater than about 15 per cent. A concentration of modifying ingredients which has been found desirable is from about 2 per cent to about 5 per cent by weight, although larger amounts up to per cent or even per cent may be found desirable.

The specific embodiments of the invention described above are intended to be illustrat ve and not limitative and it is intended that the invention include within its scope those modifications and equivalents which would be apparent to one skilled in the art.

What is claimed is:

1. An electrical resistance wire made up of an alloy having the following ingredients in the following proportions together with incidental impurities:

Per cent by wei ht Cobalt 54.5

Manganese 39.6

Copper 4.5

Aluminum 1.4

2. An electrical resistance element made up of an alloy consisting of the following ingredients 6 in the following proportions together with incidental impurities:

Per cent by weight Cobalt 50 to 60 Manganese 35 to 45 Copper 2 to 10 Aluminum 1 to 5 3. A resistance alloy containin the following ingredients in the following proportions:

Per cent by weight Cobalt 54.5

Manganese 39.6 Copper 4.5 Aluminum 1.4

4. A resistance alloy consisting of the following ingredients in the following proportions:

Per cent by weight Cobalt 50 to 60 Manganese 35 to 45 Copper 2 to 10 Aluminum 1 to 5 5. A wire-wound electrical resistor, the resistance wire of which is made up of an alloy having the following ingredients in the following proportions, together with incidental impurities:

Per cent by weight Cobalt 54.5

Manganese 39.6 Copper 4.5 Aluminum 1.4

6. A wire-wound electrical resistor, the resistance wire of which is made up of an alloy consisting of the following ingredients in the following proportions, together with incidental impurities:

Per cent by weight Cobalt 50 to 60 Manganese 35 to 45 Copper 2 to 10 Aluminum 1 to 5 EARL S. GREINER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- 

5. A WIRE-WOUND ELECTRICAL RESISTOR, THE RESISTANCE WIRE OF WHICH IS MADE UP OF AN ALLOY HAVING THE FOLLOWING INGREDIENTS IN THE FOLLOWING PROPORTIONS, TOGETHER WITH INCIDENTAL IMPURITIES: 